In order to obtain true portability in micro-computers and workstations, battery power is essential. Moreover, given the capacity versus size limitations of known batteries, it is essential to minimize total power consumption in order to extend the operating life of the batteries.
It is relatively easy to reduce battery consumption by an initial 60 to 70 percent. This initial savings can be accomplished by simply turning selected pieces of hardware off when they are not being used. The last 30 to 40 percent savings becomes increasingly more difficult to achieve, while simultaneously becoming increasingly more valuable in terms of extending battery life. This is due to the inverse relationship between battery life and battery load. Accordingly, savings that would seem trivial in off-line applications, might be momentous in a battery powered environment.
Further reduction in total power consumption may be achieved by replacing high power hardware with low power consuming hardware. Normally, however, this involves a tradeoff of performance. For example, the power consumption of random access memory (RAM) is generally a function of how fast the memory is. Very fast RAM will consume relatively large amounts of power, while slower RAM will generally use less power. Thus, while overall power consumption may be reduced in this manner, it is done at a sacrifice of performance.
In the past, computer memories have been managed for efficiency whereby infrequently needed blocks of memory were collected and paged out to disk, while frequently used blocks were collected and maintained in main memory for efficient access. U.S. Pat. Nos. 4,660,130 and 4,758,944, both to Bartley et al. are exemplary of such conventional memory management methods.